The invention relates generally to aids for visually handicapped people and in particular to electro-optical aids for such people who wish to see graphical material.
Many people with low vision problems (such as may be due to diabetic retinopathy, or from lack of blood circulation in the foveal or extrafoveal regions of the retina; or from glaucoma, etc.) may be capable of reading only text with large print. Such text generally must be specially made and typeset. Even with such text, many persons are unable to read although they are not totally blind, i.e. they are able in the coarsest sense to detect light and darkness by the use of the eye. Such visually handicapped people have used various devices and aids to help them see graphical material in a way that allows them to distinguish the information shown. For example, a magnifying glass is one of the oldest but most usual aids for reading printed text.
It has been discovered that the usual arrangement of text, namely black characters on a white page, is undesirable for certain classes of visually handicapped persons. From an optical point of view, the white background presents a high noise background for the information material. Magnification of black material on a white background with a magnifying glass or other similar passive optical systems, does not eliminate this problem.
In the particular case of persons suffering from diabetic retinopathy and extensive bleeding of the retina, blood typically enters the vitreous humor of the eye and stays for extended periods of time. This suspended blood acts as a source of light scattering and the subject in effect must peer through a reddish tinted fog. Under conventional illumination with conventional print, namely, black ink on white paper, the white background provides a large source of non-information carrying light, i.e. noise, which enters the eye and scatters off the blood platelets held in suspension. As a result, in addition to the already partially non-functional retina, the presence of scattered light reduces the modulation (or contrast) transfer function of the eye and makes even highly magnified reading material difficult to resolve.
Accordingly, it is an object of this invention to provide a magnification system that produces a large area for a visually handicapped person to view, the large area presenting some magnification of graphical material.
It is a further object of the invention to translate the graphical material into a form characterized by a relatively high signal-to-noise, or signal-to-clutter, ratio for a visually handicapped person.
It is still a further object of the invention to provide a magnification system that is easy to produce with devices currently well known to the art, and that is furthermore easy for a visually handicapped person to use.